1. Field of the Invention
The present invention relates to an image forming apparatus implemented by a distributed control system including a plurality of CPU groups having a hierarchical structure.
2. Description of the Related Art
Centralized control using one CPU is performed for printer device control of an image forming apparatus using an electrophotographic system. An increasing CPU load due to centralized control requires a higher performance CPU. In addition, as the load of the printer device rises, a bundle of control communication lines needs to be laid from a CPU board to distant load driver units and many long control communication lines are indispensable. To solve these problems, a control form is receiving a great deal of attention, in which control modules which build an electrophotographic system are assigned to sub-CPUs.
Examples of the construction of a control system by distributing respective partial module control functions to a plurality of CPUs have been proposed in several control equipment product fields other than copying machines. For example, a distributed control system is applied to the system of a vehicle and the like. However, in the distributed control system, an error needs to be detected strictly to normally operate a plurality of boards (CPUs) in collaboration with each other, unlike centralized control.
For example, Japanese Patent Laid-Open No. 2006-191338 has proposed a gateway apparatus which monitors periodic messages periodically transmitted through a plurality of buses and detects a trouble device from the communication status of the periodic messages. Japanese Patent Laid-Open No. 2002-301997 has proposed a technique of easily specifying the trouble factor of an automobile by sending pseudo control information from a trouble diagnosis apparatus.
However, these conventional techniques suffer the following problems. In the distributed control system in which a plurality of CPUs perform collaborative control, it is important to individually check the operations of the CPUs which perform collaborative control, and specify a trouble part upon generation of an error. A trouble node can be confirmed by arranging a device which intensively monitors troubles. However, a monitoring-dedicated node is required and raises the cost. In a system having a hierarchical structure, it is difficult to specify a concrete trouble part when a trouble is determined using only the traffic of an upper layer.
It is effective to detect a trouble part in the test mode. However, when the test mode is applied to an image forming apparatus, the contents of the test are limited upon generation of a paper jam by a trouble during operation. Further, it is difficult to detect a trouble part in the test mode upon generation of a dynamic timing error or in an emergency stop process during operation.